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<FONT color="green">001</FONT>    <a name="line.1"></a>
<FONT color="green">002</FONT>    /*<a name="line.2"></a>
<FONT color="green">003</FONT>     * Copyright (C) 2011 Archie L. Cobbs. All rights reserved.<a name="line.3"></a>
<FONT color="green">004</FONT>     *<a name="line.4"></a>
<FONT color="green">005</FONT>     * $Id: BigFatLock.html 89 2011-04-25 18:41:56Z archie.cobbs $<a name="line.5"></a>
<FONT color="green">006</FONT>     */<a name="line.6"></a>
<FONT color="green">007</FONT>    <a name="line.7"></a>
<FONT color="green">008</FONT>    package org.dellroad.stuff.servlet;<a name="line.8"></a>
<FONT color="green">009</FONT>    <a name="line.9"></a>
<FONT color="green">010</FONT>    import java.io.IOException;<a name="line.10"></a>
<FONT color="green">011</FONT>    import java.util.concurrent.Callable;<a name="line.11"></a>
<FONT color="green">012</FONT>    <a name="line.12"></a>
<FONT color="green">013</FONT>    import javax.servlet.FilterChain;<a name="line.13"></a>
<FONT color="green">014</FONT>    import javax.servlet.ServletException;<a name="line.14"></a>
<FONT color="green">015</FONT>    import javax.servlet.http.HttpServletRequest;<a name="line.15"></a>
<FONT color="green">016</FONT>    import javax.servlet.http.HttpServletResponse;<a name="line.16"></a>
<FONT color="green">017</FONT>    <a name="line.17"></a>
<FONT color="green">018</FONT>    import org.slf4j.Logger;<a name="line.18"></a>
<FONT color="green">019</FONT>    import org.slf4j.LoggerFactory;<a name="line.19"></a>
<FONT color="green">020</FONT>    import org.springframework.web.filter.OncePerRequestFilter;<a name="line.20"></a>
<FONT color="green">021</FONT>    <a name="line.21"></a>
<FONT color="green">022</FONT>    /**<a name="line.22"></a>
<FONT color="green">023</FONT>     * Class for serializing processing using a big fat lock.<a name="line.23"></a>
<FONT color="green">024</FONT>     *<a name="line.24"></a>
<FONT color="green">025</FONT>     * &lt;p&gt;<a name="line.25"></a>
<FONT color="green">026</FONT>     * The lock can be acquired using {@link #runWithLock}. This class can also be used as a servlet filter.<a name="line.26"></a>
<FONT color="green">027</FONT>     *<a name="line.27"></a>
<FONT color="green">028</FONT>     * &lt;p&gt;<a name="line.28"></a>
<FONT color="green">029</FONT>     * Trace-level logging for displaying lock acquire and release events is included.<a name="line.29"></a>
<FONT color="green">030</FONT>     */<a name="line.30"></a>
<FONT color="green">031</FONT>    public final class BigFatLock extends OncePerRequestFilter {<a name="line.31"></a>
<FONT color="green">032</FONT>    <a name="line.32"></a>
<FONT color="green">033</FONT>        private static final Object BIG_FAT_LOCK = new BigFatLock();<a name="line.33"></a>
<FONT color="green">034</FONT>        private static final Logger LOG = LoggerFactory.getLogger(BigFatLock.class);<a name="line.34"></a>
<FONT color="green">035</FONT>    <a name="line.35"></a>
<FONT color="green">036</FONT>        @Override<a name="line.36"></a>
<FONT color="green">037</FONT>        protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response,<a name="line.37"></a>
<FONT color="green">038</FONT>          FilterChain filterChain) throws ServletException, IOException {<a name="line.38"></a>
<FONT color="green">039</FONT>            if (LOG.isTraceEnabled()) {<a name="line.39"></a>
<FONT color="green">040</FONT>                LOG.trace("thread " + Thread.currentThread() + " waiting for " + BIG_FAT_LOCK);<a name="line.40"></a>
<FONT color="green">041</FONT>                synchronized (BIG_FAT_LOCK) {<a name="line.41"></a>
<FONT color="green">042</FONT>                    LOG.trace("thread " + Thread.currentThread() + " acquired " + BIG_FAT_LOCK);<a name="line.42"></a>
<FONT color="green">043</FONT>                    try {<a name="line.43"></a>
<FONT color="green">044</FONT>                        filterChain.doFilter(request, response);<a name="line.44"></a>
<FONT color="green">045</FONT>                    } finally {<a name="line.45"></a>
<FONT color="green">046</FONT>                        LOG.trace("thread " + Thread.currentThread() + " releasing " + BIG_FAT_LOCK);<a name="line.46"></a>
<FONT color="green">047</FONT>                    }<a name="line.47"></a>
<FONT color="green">048</FONT>                }<a name="line.48"></a>
<FONT color="green">049</FONT>            } else {<a name="line.49"></a>
<FONT color="green">050</FONT>                synchronized (BIG_FAT_LOCK) {<a name="line.50"></a>
<FONT color="green">051</FONT>                    filterChain.doFilter(request, response);<a name="line.51"></a>
<FONT color="green">052</FONT>                }<a name="line.52"></a>
<FONT color="green">053</FONT>            }<a name="line.53"></a>
<FONT color="green">054</FONT>        }<a name="line.54"></a>
<FONT color="green">055</FONT>    <a name="line.55"></a>
<FONT color="green">056</FONT>        /**<a name="line.56"></a>
<FONT color="green">057</FONT>         * Invoke the given action after acquiring the big fat lock.<a name="line.57"></a>
<FONT color="green">058</FONT>         */<a name="line.58"></a>
<FONT color="green">059</FONT>        public static void runWithLock(Runnable action) {<a name="line.59"></a>
<FONT color="green">060</FONT>            if (LOG.isTraceEnabled()) {<a name="line.60"></a>
<FONT color="green">061</FONT>                LOG.trace("thread " + Thread.currentThread() + " waiting for " + BIG_FAT_LOCK);<a name="line.61"></a>
<FONT color="green">062</FONT>                synchronized (BIG_FAT_LOCK) {<a name="line.62"></a>
<FONT color="green">063</FONT>                    LOG.trace("thread " + Thread.currentThread() + " acquired " + BIG_FAT_LOCK);<a name="line.63"></a>
<FONT color="green">064</FONT>                    try {<a name="line.64"></a>
<FONT color="green">065</FONT>                        action.run();<a name="line.65"></a>
<FONT color="green">066</FONT>                    } finally {<a name="line.66"></a>
<FONT color="green">067</FONT>                        LOG.trace("thread " + Thread.currentThread() + " releasing " + BIG_FAT_LOCK);<a name="line.67"></a>
<FONT color="green">068</FONT>                    }<a name="line.68"></a>
<FONT color="green">069</FONT>                }<a name="line.69"></a>
<FONT color="green">070</FONT>            } else {<a name="line.70"></a>
<FONT color="green">071</FONT>                synchronized (BIG_FAT_LOCK) {<a name="line.71"></a>
<FONT color="green">072</FONT>                    action.run();<a name="line.72"></a>
<FONT color="green">073</FONT>                }<a name="line.73"></a>
<FONT color="green">074</FONT>            }<a name="line.74"></a>
<FONT color="green">075</FONT>        }<a name="line.75"></a>
<FONT color="green">076</FONT>    <a name="line.76"></a>
<FONT color="green">077</FONT>        /**<a name="line.77"></a>
<FONT color="green">078</FONT>         * Invoke the given action after acquiring the big fat lock.<a name="line.78"></a>
<FONT color="green">079</FONT>         */<a name="line.79"></a>
<FONT color="green">080</FONT>        public static &lt;V&gt; V runWithLock(Callable&lt;V&gt; action) throws Exception {<a name="line.80"></a>
<FONT color="green">081</FONT>            if (LOG.isTraceEnabled()) {<a name="line.81"></a>
<FONT color="green">082</FONT>                LOG.trace("thread " + Thread.currentThread() + " waiting for " + BIG_FAT_LOCK);<a name="line.82"></a>
<FONT color="green">083</FONT>                synchronized (BIG_FAT_LOCK) {<a name="line.83"></a>
<FONT color="green">084</FONT>                    LOG.trace("thread " + Thread.currentThread() + " acquired " + BIG_FAT_LOCK);<a name="line.84"></a>
<FONT color="green">085</FONT>                    try {<a name="line.85"></a>
<FONT color="green">086</FONT>                        return action.call();<a name="line.86"></a>
<FONT color="green">087</FONT>                    } finally {<a name="line.87"></a>
<FONT color="green">088</FONT>                        LOG.trace("thread " + Thread.currentThread() + " releasing " + BIG_FAT_LOCK);<a name="line.88"></a>
<FONT color="green">089</FONT>                    }<a name="line.89"></a>
<FONT color="green">090</FONT>                }<a name="line.90"></a>
<FONT color="green">091</FONT>            } else {<a name="line.91"></a>
<FONT color="green">092</FONT>                synchronized (BIG_FAT_LOCK) {<a name="line.92"></a>
<FONT color="green">093</FONT>                    return action.call();<a name="line.93"></a>
<FONT color="green">094</FONT>                }<a name="line.94"></a>
<FONT color="green">095</FONT>            }<a name="line.95"></a>
<FONT color="green">096</FONT>        }<a name="line.96"></a>
<FONT color="green">097</FONT>    <a name="line.97"></a>
<FONT color="green">098</FONT>        /**<a name="line.98"></a>
<FONT color="green">099</FONT>         * Verify that the current thread is holding the big fat lock.<a name="line.99"></a>
<FONT color="green">100</FONT>         */<a name="line.100"></a>
<FONT color="green">101</FONT>        public static boolean isLockHeld() {<a name="line.101"></a>
<FONT color="green">102</FONT>            return Thread.holdsLock(BIG_FAT_LOCK);<a name="line.102"></a>
<FONT color="green">103</FONT>        }<a name="line.103"></a>
<FONT color="green">104</FONT>    <a name="line.104"></a>
<FONT color="green">105</FONT>        @Override<a name="line.105"></a>
<FONT color="green">106</FONT>        public String toString() {<a name="line.106"></a>
<FONT color="green">107</FONT>            return "BigFatLock@" + System.identityHashCode(this);<a name="line.107"></a>
<FONT color="green">108</FONT>        }<a name="line.108"></a>
<FONT color="green">109</FONT>    }<a name="line.109"></a>
<FONT color="green">110</FONT>    <a name="line.110"></a>




























































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